[PATCH 4/4] workqueue: handle change in cpu-node relationship.

[Kamezawa Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>]

Although workqueue detects relationship between cpu<->node at boot,
it is finally determined in cpu_up().
This patch tries to update pool->node using online status of cpus.

1. When a node goes down, clear per-cpu pool's node attr.
2. When a cpu comes up, update per-cpu pool's node attr.
3. When a cpu comes up, update possinle node cpumask workqueue is using for sched.
4. Detect the best node for unbound pool's cpumask using the latest info.

Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
---
 kernel/workqueue.c | 67 ++++++++++++++++++++++++++++++++++++++++++------------
 1 file changed, 53 insertions(+), 14 deletions(-)

diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index 07b4eb5..259b3ba 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -266,7 +266,8 @@ struct workqueue_struct {
 static struct kmem_cache *pwq_cache;
 
 static cpumask_var_t *wq_numa_possible_cpumask;
-					/* possible CPUs of each node */
+	/* possible CPUs of each node initialized with possible info at boot.
+           but modified at cpu hotplug to be adjusted to real info.  */
 
 static bool wq_disable_numa;
 module_param_named(disable_numa, wq_disable_numa, bool, 0444);
@@ -3449,6 +3450,31 @@ static void put_unbound_pool(struct worker_pool *pool)
 	call_rcu_sched(&pool->rcu, rcu_free_pool);
 }
 
+/*
+ * detect best node for given cpumask.
+ */
+static int pool_detect_best_node(const struct cpumask *cpumask)
+{
+	int node, best, match, selected;
+	static struct cpumask andmask; /* we're under mutex */
+
+	/* Is any node okay ? */
+	if (!wq_numa_enabled ||
+	    cpumask_subset(cpu_online_mask, cpumask))
+		return NUMA_NO_NODE;
+	best = 0;
+	selected = NUMA_NO_NODE;
+	/* select a node which contains the most cpu of cpumask */
+	for_each_node_state(node, N_ONLINE) {
+		cpumask_and(&andmask, cpumask, cpumask_of_node(node));
+		match = cpumask_weight(&andmask);
+		if (match > best)
+			selected = node;
+	}
+	return selected;
+}
+
+
 /**
  * get_unbound_pool - get a worker_pool with the specified attributes
  * @attrs: the attributes of the worker_pool to get
@@ -3467,7 +3493,6 @@ static struct worker_pool *get_unbound_pool(const struct workqueue_attrs *attrs)
 {
 	u32 hash = wqattrs_hash(attrs);
 	struct worker_pool *pool;
-	int node;
 
 	lockdep_assert_held(&wq_pool_mutex);
 
@@ -3492,17 +3517,7 @@ static struct worker_pool *get_unbound_pool(const struct workqueue_attrs *attrs)
 	 * 'struct workqueue_attrs' comments for detail.
 	 */
 	pool->attrs->no_numa = false;
-
-	/* if cpumask is contained inside a NUMA node, we belong to that node */
-	if (wq_numa_enabled) {
-		for_each_node(node) {
-			if (cpumask_subset(pool->attrs->cpumask,
-					   wq_numa_possible_cpumask[node])) {
-				pool->node = node;
-				break;
-			}
-		}
-	}
+	pool->node = pool_detect_best_node(pool->attrs->cpumask);
 
 	if (worker_pool_assign_id(pool) < 0)
 		goto fail;
@@ -4567,7 +4582,7 @@ static int workqueue_cpu_up_callback(struct notifier_block *nfb,
 	int cpu = (unsigned long)hcpu;
 	struct worker_pool *pool;
 	struct workqueue_struct *wq;
-	int pi;
+	int pi, node;
 
 	switch (action & ~CPU_TASKS_FROZEN) {
 	case CPU_UP_PREPARE:
@@ -4583,6 +4598,16 @@ static int workqueue_cpu_up_callback(struct notifier_block *nfb,
 	case CPU_ONLINE:
 		mutex_lock(&wq_pool_mutex);
 
+		/* now cpu <-> node info is established, update the info. */
+		if (!wq_disable_numa) {
+			for_each_node_state(node, N_POSSIBLE)
+				cpumask_clear_cpu(cpu,
+					wq_numa_possible_cpumask[node]);
+			node = cpu_to_node(cpu);
+			cpumask_set_cpu(cpu, wq_numa_possible_cpumask[node]);
+		}
+		for_each_cpu_worker_pool(pool, cpu)
+			pool->node = cpu_to_node(cpu);
 		for_each_pool(pool, pi) {
 			mutex_lock(&pool->attach_mutex);
 
@@ -4951,7 +4976,21 @@ void workqueue_register_numanode(int nid)
 void workqueue_unregister_numanode(int nid)
 {
 	struct workqueue_struct *wq;
+	const struct cpumask *nodecpumask;
+	struct worker_pool *pool;
+	int cpu;
 
+	/* at this point, cpu-to-node relationship is not lost */
+	nodecpumask = cpumask_of_node(nid);
+	for_each_cpu(cpu, nodecpumask) {
+		/*
+		 * pool is allcated at boot and assumed to be persistent,
+		 * we cannot free this.
+		 * Update to be NUMA_NO_NODE. This will be fixed at ONLINE
+		 */
+		for_each_cpu_worker_pool(pool, cpu)
+			pool->node = NUMA_NO_NODE;
+	}
 	mutex_lock(&wq_pool_mutex);
 	list_for_each_entry(wq, &workqueues, list)
 		wq_release_unbound_numa(wq, nid);
-- 
1.8.3.1